Do grossly identifiable ganglia lie along the spinal accessory nerve? A gross and histologic study with potential neurosurgical significance

Objective: To elucidate further the anatomy of focal enlargements that have been observed along the spinal accessory nerve (SAN) as it courses within the posterior cranial fossa. Methods: Dissection of the posterior cranial fossa was performed on 27 adult cadavers with attention to the SAN and any focal enlargements associated with it. Results: Grossly, four specimens (14.8%) were found to have focal enlargements associated with the SAN within the posterior cranial fossa. These structures were in intimate contact with the dorsal aspect of the spinal portion of the SAN in all specimens and measured a mean diameter of 1.9 mm. One right-sided male specimen had two focal enlargements. All focal enlargements were found within 1 cm of the foramen magnum. Histologically, no ganglion or neuronal cells were identified within these focal enlargements in any specimen. These focal enlargements are best described as ectopic glial nests or heterotopias within the leptomeninges around the SAN. Conclusions: The focal enlargements located along the SAN should not be termed ganglia. These structures do not contain neural structures and should not be mistaken for pathology of the posterior fossa.